Catalytic process for the preparation of organic compounds



Patented June 26, 1934 UNITED STATES CATALYTIC PROCESS FOR THE PREPARA- TION OF ORGANIC COMPOUNDS Wilbur A. Lazier, Elmhurst, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 23, 1930, Serial No. 470,238

16 Claims. (Cl. 260106) This invention relates to the preparation and use of improved catalyst compositions, and more particularly to promoted chromite catalysts which are especially suitable for the carrying out of organic hydrogenation and dehydrogenation reactions.

This case is a continuation in part of my copending application Serial No.'285,501, filed June 14, 1928 which has matured into U. S. Patent No.

1,857,921, May 10, 1932.

The rapid development of technically successful processes of synthesizing useful organic compounds from water gas has led to the proposed use of numerous combinations and mixtures of various catalytic metals and metallic oxides. In general, such catalyst compositions as have been suggested have consisted of two or more elements or compounds in the form of intimate physical mixtures, such as those formed by the co-precipitation of hydroxides or salts. A typical and widely used catalyst of this type is prepared by co-precipitating a mixture of zinc hydroxide and chromium hydroxide with a base, or by mixing chromic acid with an excess of zinc oxide. According to U. S. Patent 1,746,782 issued to'meon February 11, .1930, particularly useful catalyst compositions are obtained by igniting at a red heat chromates of various hydrogenating metals to form chromites containing the hydrogenating metal oxide partially combined with chromium sesqui-oxide to form loosely bound but very refractory compounds of indefinite chemical composition which may be classified under the term chromites.

Another convenient method of preparing these important chromite catalysts consists of heating a double salt of a hydrogenating metal and a nitrogen base, such as ammonia, to its spontaneous decomposition temperature, as disclosed in Patent 40 1,746,783. For example, basic zinc ammonium chromate when heated to 400 C., undergoes an exothermic gaseous decomposition resulting in a finely divided, powdery, black residue of zinc chromite containing free zinc oxide as well as zinc oxide combined with chromium sesqui-oxide. These simple chromite compositions when used alone as catalysts for various organic hydrogenation and dehydrogenation reactions, have beenv found to be particularly effective. However, so far as I am aware, no mixed or promoted multiple chromite catalysts containing a plurality of chromites of hydrogenating metals have been developed or applied in such catalytic hydrogenations or dehydrogenations previous to my inven-' tion.

This invention has as an object to provide a new catalyst composition which is particularly effective in catalyzing a variety of organic chemical reactions, especially those involving the hydrogenation of unsaturated carbon compounds, the dehydrogenation of oxygenated organic compounds, such as the alcohols and other hydrogen ations and dehydrogenations in general. A further object is to provide a promoted catalyst composition comprising a mixture of various hydrogenating metals in the form of their oxides or chromites, said composition having as a whole a catalytic effect in the various reactions to which it is applied greater than the sum of the effects of its constituent oxides or chromites. A still further object is to carry out catalytic organic hydrogenation and dehydrogenation reactions more efficiently than heretofore by the aid of these mixed chromite compositions. It is a specific object to carry out the high pressure dehydrogenation of ethyl alcohol to form ethyl acetate by employing a mixedchromite catalyst prepared according to this invention.

These objects are accomplished by. the following invention which, in its general aspects, comprises mixing or intimately associating a small amount of an oxide or chromite of one or more hydrogenating metals whose oxides are readily reducible with a chromite of one or more hydrogenating metals whose oxides are difiicultly reducible, and the application 'of the resulting mixed or promoted catalyst to various organic hydrogenation and dehydrogenation reactions. The invention also contemplates various combinations or mixtures of chromites of diflicultly reducible hydrogenating metal oxides and easily reducible hydrogenating metal oxides, as well as mixtures or combinations of various easily reducible hydrogenating metal oxides, in widely varying proportions of the respective constituents.

In the following examples I have set forth in detail several catalyst compositions prepared in accordance with the principles of my invention, together with methods for their employment in various catalytic reactions, and also comparative data showing the improvement effected through their use. These examples are presented only for purposes of illustration and are notto be regarded as limitations.

Example 1.A cadmium promoted zinc chromite catalyst was prepared as follows: 62 grams of cadmium nitrate was dissolved in 150 cc. of water and added to a solution of 574 grams of crystallized zinc sulphate dissolved in two liters of water. To this mixed solution there was'added with stirring 2.2 liters of neutral ammonium chromate solution containing 305 grams of tion of considerable heat, ammonia, and oxides of nitrogen, resulting in about a 25% less in weight and leaving behind an almost black, powdery residue containing the oxides of zinc and cad-= mium partially combined with chromium sesquioxide in' the form of chromites. The chromium was substantially all converted by the heating process from the hexavalent to the trivalent form. In order, to give the promoted catalyst suit-' able form, it was compressed into tablets which were broken up and the grains screened to 6-14 mesh.

The activity of the above described catalyst was tested by employing it in the catalytic dehydrogenation of ethyl alcohol vapor at atmospheric pressure as follows: One cc. of the catalyst was placed in a glass reaction tube having a diameter of 15 mm. in such a. manner as to form a discshaped catalytic screen held in place with plugs of glass wool. The tube was heated at 400 C. and absolute ethanol vapor waspassed therethrough at the rate of 50 cc. of liquid alcohol per hour. There was formed per hour 4.5 liters of gas measured at ordinary conditions of temperature and pressure, consisting of 5% ethylene and 95% hydrogen, representing a conversion of 1% of the alcohol to ethylene and water and 19.7% to acetaldehyde and hydrogen, or an overall conversion of about 20.7%.

By way of showing the improvement to be obtained by-the addition of a small amount of cadmium to'the above catalyst-composition, a plain .zinc chromite catalyst prepared by the method described, but without the use of cadmium, when employed in the same manner in the same testing equipment, gave only 3.5 liters of gas having the same composition as indicated above, representinga total conversion of the alcohol of only about 16%. It will be seen. therefore, that the addition of cadmium to the zinc chromite catalyst caused a 29% improvement in activity toward this particular reaction.

Example 2.-A solution containing 190 grams of zinc nitrate and 12 grams of copper nitrate dissolved in one liter of water was treated with a solution prepared by dissolving 160 grams of ammonium chromate and 50 cc. of ammonium hydroxide in one liter of water. The resulting brownish yellow precipitate was filtered, dried without washing and ignited for two hours at 400 C. while being'ireely exposed to air, after which the residue weighed 155 grams. The bluish, black copper-zinc chromite resulting from r the ignition was briquetted and screened to 6-14 mesh grains.

A copper-zinc chromite catalyst obtained as just described was employed for the catalytic synthesis of methanol from water gas containing 50% hydrogen, 34% carbon monoxide, 1.5% carbon dioxide and 1% of methane and nitrogen. A

portion of the catalyst was placed in a pressure resisting tube and heated to 352 C. At this temperature the water gas was passed through the tube at the rate of 20,000 volumes of gas, measured at ordinary'conditions of temperature and pressure, per unit volume of catalyst per hour and at a pressure of 267 atmospheres. There was formed per 100 cc. of'catalyst per hour 136 cc. of crude condensate containing pure methanol.

The improvement in activity due to the presence of the copper is shown by the fact that a plain zinc chromite catalyst prepared exactly as just described, but without the addition of copper, when employed in methanol synthesis under similar conditions of temperature, pressure, and gas composition, gave per cc. oi catalyst per hour only 114 cc. of crude condensate containing 86% methanol.

Example 3.-A special study was made of the efiect of cadmium, lead, and bismuth when incorporated separately into zinc chromite catalysts employed for the high pressure dehydrogenation of ethanol, wherein ethyl acetate is formed as the major product of'the reaction.

The plain-zinc chromite control catalystand the three promoted zinc chromites containing the various metals just mentioned were all made in the same manner by precipitating 2-molar solutions of the base metal salts with an equivalent amount of 2-molar neutral ammonium chromate solutions, followed by neutralization with ammonia, washing by decantation, filtering, drying and igniting at 400 C. 1

The plain zinc chromite catalyst was prepared from zinc sulphate. The cadmium-zinc chromite composition was prepared from a solution containing 25 mole percent cadmium nitrate and 75 mole percent zinc sulphate. The lead-zinc chromite combination was prepared from a solution containing 10 mole percent lead nitrate and 90 mole percent zinc nitrate. The bismuth-zinc chromite catalyst was prepared from a solution containing 10 mole percent bismuth nitrate and 90 mole percent zinc nitrate.

Test runs on each of the four catalysts were carried out as follows: 25 cc. of the catalyst undergoing investigation was loaded into a acetaldehyde, acetone, butanol, crotonyl alcohol,

and esters higher in molecular weight than ethyl acetate, the following table shows the relative activities of the various catalysts as measured by the ester content of the condensate calculated as weight percent of alcohol converted to ethyl acetate:

It is to be noted that with each of the catalysts containing. as a promoter 9. hydrogenating metal having a reducible oxide, the yield of ester is substantially greater than with zinc chromite alone.

Example 4.Maximum conversion of ethanol to ethyl acetate by high pressure dehydrogenation was obtained when a zinc chromite catalyst promoted with both copper and cadmium was employed in an elongated reaction tube heated by means of a vapor bath maintained at a carefully controlled temperature.

The catalyst was prepared by precipitating a mixed solution containing 82.5 mole percent of zinc sulphate, 10 mole percent copper sulphate and 7.5 mole percent cadmium nitrate with a chemically equivalent amount of ammonium chromate freshly prepared from chromic acid and ammonia. The multiple chromates, containing also ammonium chromate, were washed, dried, and ignited at 400 C. to form a black powder containing the chromium oxide still uncombined with the base metals, but existing substantially in the trivalent form. This chromite material was briquetted, crushed, and screened to 14-18 mesh material.

cc. of the finely grained catalyst was loaded into a cylindrical cartridge which was placed in a vapor heated pressure resisting jacket. As in Example 3, ethyl alcohol was pumped therethrough at the rate of 400 cc. per hour. The catalyst temperature was maintained at 380 C. and the pressure at 204' atmospheres. The liquid condensate contained esters equivalent to a' conversion to ethyl acetate of 25 weight percent of the alcohol injected. In addition, the condensate contained a little acetaldehyde and acetone and 5.8% of material boiling above 100 C. consisting of about 25% 4-carbon alcohols, 23% acetic acid, ethyl butyrate and butyl acetate and some higher boiling compounds.

The very high conversion of ethyl alcohol to ethyl acetate obtained was due to the extraordinary eflicacy of the three-component chromite composition, containing a lesser amount of the chromites of two hydrogenating metals having easily reducible oxides and a greater amount of a chromite of a hydrogenating metal having a difficulty reducible oxide.

That the improvement obtained is not the average of the catalytic effects of the various constituent chromites of the composition, as would be expected from a consideration of the eifects of the individual components when acting separately, is shown by the following table in which the conversions of the respective single chromites are given. ,It is also shown that no two-compoa nent chromite catalysts containing 10' mole percent of the promoting chromites were equal in activity to the preferred three-component chromite catalysts of the above example. The tests were made in the same equipment and under the same conditions outlined above, and the catalysts were prepared by the same general method already described.

ExampZe5.Nickel and zinc ammonium chromates were prepared by dissolving 297 grams of zinc nitrate and 290 grams of nickel nitrate in 2.0 liters of-water, adding a solution of 250 grams of ammonium bichromate and 350 cc. of ammonium hydroxide in two liters of water and heating to boiling. The resulting precipitate was washed, filtered, dried and heated to its spontaneous decomposition temperature, after which the resulting black residue was reduced in hydrogen at 300-475 C. The final composition contained 13% elementary nickel.

When used in liquidphase hydrogenation, 10 grams of this catalyst caused the rapid absorption of hydrogen by solution of 100 grams of glucose in 100 cc. of water at a temperature of 150 C. and at a pressure of 1000 pounds. Sorbitol was formed quantitatively.

Example 6.A hydrogenation catalysts is prepared as follows: 23 grams of cadmium nitrate, 24 grams of copper nitrate, and 245 grams of zinc nitrate are dissolved in 500 cc. of water and mixed at ordinary temperature with an equal volume of water containing 126 grams of ammonium bichromate and cc. of 28% ammonium hydroxide. After stirring, the mixture is exactly neutralized with additional ammonium hydroxide and allowed to settle. After several washes by decantation, the precipitate is dried, ignited at 400 C. and compressed into tablets or grains suitable for use in catalytic gas apparatus.

25 cc. of the mixed chromite catalyst prepared as above was loaded into analloy steel reaction vessel capable of being heated and withstanding high pressures. heater, a pump for injecting liquid at a constant rate, a T connection for introducing hydrogen under pressure, a suitable condenser and trap for separating liquid products, and exit control valves. v

A sample of 93% n-butyl n-butyrate was subjected to hydrogenation over the catalyst prepared as just indicated. The rate of flow was 700 cc. of ester per 100 cc. of catalyst per hour. The system was heated to 346 C. and maintained at a pressure of 2600-3600 pounds. The hydrogen-ester molecular ratio was 13.8. From 710 cc. of the butyrate so treated there was obtained by distillation 580 cc. of pure normal butanol boiling at 117 C., representing a conversion of the ester to butanol of approximately 73% of the theoretical.

Although in the above examples I h'aveindicated certain definite conditions of temperature, pressure, gas velocity, amounts of materials,

duration of reactions, etc., it is to be understood that any and all of these may be varied widely within the scope of my invention, since the particular conditions of operation are governed largely by the specific reaction, the materials treated, and the catalysts composition selected for a given reaction.

The promoted chromite catalysts, which: are the subject of this invention, may be prepared by various methods. For example, they may be prepared by heating a mixture ofcompounds containing one or more hydrogenatingmetals The tube is fittedwith a pre-' whose oxides are reducible by hydrogen, one or more hydrogenating metals whose oxides are difficultly reducible or non-reducible by hydrogen and hexavalent chromium, to a temperature sufficient to cause the chromium to be reduced substantially to the trivalent form. I may, for example, prepare a mixture of copper chromate and zinc chromate and ignite the mixture at a red heat, that-is to say, a temperature of 600 C. or I above, in order to drive off oxygen and form a .mixture of copper oxide, zinc oxide, copper chromite. and zinc chromite. A more convenient cobalt and nickel.

method consists of co-precipitating multiple chromates of the reducible and non-reducible oxides with ammonium chromate whereby double ammonium chromates are formed which decompose spontaneously and exothermically when heated to about 400 C.

By hydrogenating metals and oxides, I refer to those metals and oxides which are capable under proper conditions of serving as catalysts for the addition of hydrogen to such unsaturated compounds as ketones or olefins, or are capable of inducing the dehydrogenation of alcohols in the vapor phase in preference to dehydration.

By diificultly reducible-oxides, I refer to those which remain substantially in the oxide form after several hours exposure in a pure state to the action of hydrogen at 400 C. Reducible oxides under the same conditions are readily converted to the elementary metal and water vapor.' Suitable hydrogenating metals whose oxides are readily reducible are silver, cadmium, copper, lead, mercury, tin, bismuth, indium, iron, Hydrogenating metals whose oxides are diflicultly reducible are magnesium,

zinc and manganese.

I have referred herein several times to promoters. By this term I refer toa metal or metals, either in the metallic state or in the form of an oxide or other compound, which is added to a simple hydrogenating metal chromite, such as zinc chromite for the purpose ofincreasing its propensity to catalyze certain reactions, such as the hydrogenation or dehydrogenation of certain organic compounds. As indicated elsewhere,

. the effect of such addition in the case of the compositions forming the subject matter of this invention is to give the resulting composition a catalytic effect which is considerably greater than the sum of the effects of the various constitu-- ents; In other words, the catalytic effect of the catalyst is not merely the additive effect of these components.

According to the principles of my inventon, a single metal having an easily reducible oxide may be used in. conjunction with the simple chromites, or a plurality of such metals may be employed. Among those mentioned above, copper and cadmium are particularly useful, either when used alone or in combination. I have found that especially good results are obtained when a copper-cadmium-zincchromite combination is employed.-

The amount of promoter maybe varied within wide limits. In general, I prefer to use much less reducible metal oxide than catalytic non-re ducible oxide. Suitable concentrations are found between 1 and 25 mole percent of the total base metal used. It is to be understood, however, that reducible oxides are not nearly so susceptible to reduction when combined wholly or in part with chromium oxide to form chromites as they are when not so combined. For example, a zinc chromite catalyst promoted with copper may be rather inert to reductionafter which the copper is still contained largelyin the oxide form.

The promoted chromite catalyst compositions which are the subject of this invention may be characterized as finely divided, refractory, dark colored powders containing chromium sesquioxide rather completely combined with a greater proportion of a hydrogenating metal whose oxide is diflicultly reducible and a lesser proportion of a promoting hydrogenating metal whose oxide is easily reducible. Base metal oxides may or may not be present in excess of the amount necess'ary to form chromites with the chromium oxide. The term chromite as here used does not necessarily refer to a compound of definite chemical composition, since the-chromites, in the sense of this invention, may contain widely difiering proportions of their components and yet be substantially combined.

By mea'nsof acid extraction I have been able to prove that in these chromite compositions, compound formation exists between a part of the base metal oxides and the chromium sesqui-oxide. For example, zinc oxide is completely soluble in 10% acetic acid. .Likewise, a catalyst mixture prepared by co-precipitation of zinc hydroxide and chromium hydroxide yields substantially all 9( lute acetic acid, the residual product contained 9:

41% of zinc oxide in the form of an acid resistant chromite compound. The same phenomenon is observed with mixed chromites and demonstrates the chemical nature of the product. The hydrogenating metal may exist, for example, 104 either. in the metallic form, or as an oxide, or both. The chemical relationships of the various elements of the composition depend to a certain extent upon the methods of preparation and reduction employed.

I have disclosed above several methods of preparation of promoted chromite catalysts, including the heating to their spontaneous decomposition temperature of mixtures of certain double ammonium chromates of various hydrogenating 11 metals.

The promoted chromite catalyst compositions of my invention are applicable to a wide variety of catalytic reactions, but particularly to those involving hydrogenation or dehydrogenation of 1] organic or other carbon compounds. They are particularly suitable for the dehydrogenation of alcohols at ordinary or higher pressures, the catalytic hydrogenation of esters under pressure to form the corresponding alcohols, the synthesis of methanol and higher alcohols from oxides of carbon and hydrogen, the hydrogenation of aldehydes or ketones under pressure, and the conversion of carbon monoxide and steam to carbon dioxide and hydrogen (the water gas reaction).

-As many apparently and widely different embodiments of this invention may be made without departing from the spirit and scope thereof,. it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim: 7 I

1. In a catalytic process of forming organic compounds in a three component reaction system 1 comprising a mixture consisting of an oxygencontaining carbon compound capable of hydrogenation, an oxygen-containing carbon compound capable of dehydrogenation, and hydrogen, the step which comprises bringing the mixture 1 into contactwith a catalyst composition containing essentially a plurality of hydrogenating metal chromites.

2. The process of claim 1 in which the catalyst is a composition comprising a plurality of hydro- I genating metals, including a hydrogenating metal whose oxide is difiicultly reducible and a hydrogenating metal whose oxide is easily reducible, both of which are associatedwith and at least partially combined with chromium sesqui-oxide. j

3. The process of claim 1 in which the catalyst contains zinc chromite and a chromite of a metal having an easily reducible oxide.

4. The process of claim 1 in which the catalyst comprises a mixture of zinc, copper and cadmium chromites.

5. The process of claim 1 in which the catalyst is prepared by igniting a mixture of hydrogenating metal chromates.

6. The process of claim 1 in which the catalyst is prepared by igniting a mixture of double chromates of hyd'rogenating metals and nitrogen bases.

'7. The process of claim 1 in which the temperature is maintained above 346 C. and the pressure is superatmospheric.

8.'In the process of converting a primary alcohol into the corresponding ester in the presence of a catalyst and under an elevated temperature and pressure, the step which comprises bringing the primary alcohol into contact with a catalyst containing essentially a composite mixture of hydrogenating metal chromites.

9. The process of claim 8 in which the catalyst is a composition comprising a plurality of hydrogenating metals, including a hydrogenating metal whose oxide is difiicultly reducible and a hydrogenating metal whose oxide is easily reducible, both of which are associated and at least partially combined with chromium s'esqui-oxide.

10. The process of claim 8 in which the catalyst contains zinc, copper and cadmium chromites.

11..The process of converting ethyl alcohol to ethyl acetate and other organic products including butyl alcohol, acetaldehyde and hydrogen, which comprises conducting the vapor of said alcohol at a temperature of 340 C. to 410 C. and a pressure of 10 to 500 atmospheres over a catalyst composition comprising a composite mixture of zinc chromite, copper chromite and cadmium chromite.

12. The process of claim 11 in which the catalyst contains a chromite of a hydrogenating metal having a diificulty reducible oxide and a chromite of a hydrogenati'ngmetal' having an easily reducible oxide.

'13. The process of claim 11 in which the catalyst contains zinc, copper and cadmium chromites.

14. In the process of making methanol from a gaseous mixture of carbon monoxide and hydrogen, the step which comprises passing the mixture over a catalyst composition comprising a plurality of hydrogenating metal chromites.

15. The process of converting an ester of an aliphatic carboxylic acid containing more than one carbon atom into the corresponding alcohol which comprises heating a mixture of said ester and hydrogen to an elevated temperature at an elevated pressure in the presence of a catalyst composition comprising a plurality of hydrogenating metals, including a hydrogenating metal whose oxide is difiiculty reducible and a hydrogenating metal whose oxide is easily reducible, bothof which are associated with and at least partially combined with chromium sesqui-oxide.

16. The process of claim 15 in which the catalyst contains a"mixture of Zinc, copperand cadmium chromites. V

WILBUR. A. LAZIER. 

